Summary

Gas-well performance forecasting during boundary-dominated flow (BDF) islargely based on the application of pseudopressure, pseudotime, andmaterial-balance-pseudotime concepts to rate, pressure, and time data.Recently, Ayala H. and Ye (2012; 2013) and Ye and Ayala H. (2013) demonstratedthe convenience and importance of a rescaled exponential model thatsuccessfully forecasted gas-well decline in BDF by use of density-baseddimensionless parameters in place of pseudovariables. In this study, theinterdependability and interchangeability of these methodologies is formallydemonstrated with a rigorous derivation for rescaled exponential models on thebasis of fundamental physical principles applicable to BDF conditions. Therescaled exponential equation is demonstrated to be a rigorous rate/timeequation modeling gas-rate decline in wells produced against aconstant-bottomhole-pressure specification. The proposed BDF decline equationis shown to be able to be expressed in terms of a dimensionless fluid parameter(¯B) that quantifies the µgcg dependency ondensity for the depletion process of interest, which has been directly tied tothe hyperbolic decline coefficient experienced by a declining gas well. Casestudies are presented to demonstrate the capabilities of the rescaledexponential model for gas-rate forecasting for wells producing at a constantbottomhole pressure, and its performance is compared to all other availablemodels in the literature.